Answer / pillay

A typical 3 phase motor has 3 sets of windings. Each set of
windings have 2 terminals namely the start and the end of
the winding.During the start the end of of all 3 windings
is joined together through a contactor known as the star
contactor and the 3 phase power supply is applied across the
start terminals of the 3 windings.This windings are actually
designed for the application of 2 different phase voltages
across them.So during start up lower voltage is applied and
so a lower current is drawn. but after a few seconds the
connections are changed through the change over of
contactors to the full voltage across the windings known as
delta connections. This start and change over is done by
timer controlled contactors.

Answer / hiren bhatt

in star connection line voltage of system is decreased to 1
by square root of 3 is equal to 1/1.73 of line voltage,
thats why in starting motor get reduced voltage asper this
ratio and hence star connection help to reduce effect of
dv/dt to the connected load and hence its insulation and
starting current protected

Answer / devi kumar

star resistance have more than delta resistance ex:star have 4 ohms delta 2 Ohms so I=V/R star current =230/4 57.5
Delta current = 230/2 = 115

Can we transmit digital signal to long distance ?

0 Answers  

---

From, which load current range ( upper - lower limit current)can Air circuit breaker used for in electrical circuit.

4 Answers   ABC,

---

why do we use UPF watt meter in short circuit test of the transformer and LPF watt meter in open circuit test of the transformer

2 Answers   Bell, TCS,

---

Sir we are using 250 kva DG its Diesel consumption 25 lits / hrs maximum load 160 kva now how to calculate units/ litres

1 Answers  

---

In DC motor,the field MMF is given by NI.N-no.of field winding turns,I-excitation and both are constant.Then how could the main flux decreases due to armature reaction.

4 Answers   Bhel, IBM,

---

High Voltage out door substation-annual maintenance, things to be considered

1 Answers  

---

What is the out put of a CT? How the ratio is decided ?

1 Answers  

---

We use MCCB not MCB for motor starters because MCCBs has capablity to drawout the motor starting current which is 5-6 times the full load current of motor for 1sec. Then why we use SDF in starter panel means MCC panels. Pls reply if any one knows this answer.

1 Answers  

---

What is the effect of positive feedback on the stability of the systems?

0 Answers  

---

if z transform lies in ROC then. a)system is stable b)inverse of system is stable c)both system and its inverse are stable.

1 Answers   CCP,

---

As per the theory current doesn’t flows in Neutral, but practically it is not applicable, explain why?

3 Answers  

---

can I improve the furnace power factor (10 mva transformer) by adding a capacitor bank before the transformer.Does system power factor vary a lot with the furnace PF?

0 Answers  

---